(a) Field of the Invention
The present invention relates to a liquid crystal display (LCD), more specifically to an LCD having an electrode array for generating electric fields in a signal substrate.
(b) Description of the Related Art
A liquid crystal display having an electrode array for generating an electric field which is parallel to both substrates (IPS-mode in-plane switching mode) is described in U.S. Pat. No. 5,598,285. However, this IPS-mode LCD has several problems.
The first problem is that the height difference of the two electrodes, a common electrode and a pixel electrode used for generating electric fields, causes uneven rubbing of an alignment layer, which results in the light leakage.
The second problem is that the potential difference between a data line applying data signals to the pixel electrode, and the common electrode in the region between them may cause some light leakage and the light leakage is also causing the lateral cross talk.
To prevent any light leakage, the width of a black matrix along the perimeter of a pixel region may be widened, or the gap between the common electrode and the data line may be narrowed. However, the aperture ratio of the LCD is reduced when the black matrix is widened, and the common electrode and the data line may easily short when the gap between the common electrode and the data line is made smaller.
The third problem is that the contact property of pads connected to signal lines, which are usually made of an aluminum or an aluminum alloy having low resistivity, is poor, because the aluminum or aluminum alloy, when exposed, is easily oxidized.
In view of the above, it is an object of the present invention to prevent any light leakage in an LCD.
It is another object of the present invention to reduce the disconnections of the signal lines and to prevent the shorts between a data line and a common electrode.
It is another object of the present invention to increase the aperture ratio of an LCD and to improve the contact property of the pads.
These and other objects, features and advantages are provided, according to the present invention, by making a data line to have a double-layered structure, and by overlapping common electrodes adjacent to the data line with one layer of the data line.
The data line may include a lower layer, which is made of the same layer as a pixel electrode, and an upper layer formed of a pad material which is not easily broken in the manufacturing process.
To provide these and other objects, features and advantages, in the substrate for an IPS-mode LCD according to the present invention, are provided by including a gate line and an array of common electrodes formed on a transparent insulating substrate, and a first insulating layer covering the gate line and the common electrodes. A first and a second data lines, are formed on the first insulating layer. The first and the second data lines overlap each other and are connected to each other through a first contact hole formed in a second insulating layer interposed between the first and the second data lines. The first and the second data lines intersect the gate line. A plurality of pixel electrodes parallel to the common electrodes are formed on the first and the second insulating layer. The common electrodes adjacent to the first and second data lines, overlap the first or the second data line via the first and the second insulating layer, and the pixel electrodes may be connected to either the first or the second data line. Furthermore, a first and a second data pads, which are connected to the first and the second data lines, respectively, are connected to each other through a second contact hole formed in the second insulating layer, and a supplementary gate pad is connected to a gate pad connected to the gate line, through a third contact hole formed in the first insulating layer.
The first or the second data line and the common electrodes adjacent thereto, which overlap each other, block the light passing through the region between them, and replace a black matrix.
Furthermore, the short between the first or the second data lines and the common electrodes, is decreased, because the first and second insulating layers are interposed between the common electrodes and the first and the second data lines. The disconnections of the data line are reduced due to its double-layered structure.
The upper one among the first and the second data pads, the gate pad, the supplementary gate pad may be formed of a pad material, which are not easily damaged in the manufacturing process, such as chromium, molybdenum, molybdenum alloy or indium tin oxide (ITO).